The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 100 42 906.8, filed on Aug. 31, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a pressing arrangement for treating a fibrous material web, in particular a paper, cardboard, or tissue web, in a press nip formed between a shoe press roll and an opposing surface and elongated in the web travel direction.
2. Discussion of Background Information
As a rule, the fibrous material web is guided through the press nip with at least one dewatering belt, for example, a felt.
In the pressing arrangements of the type mentioned at the outset that have been common up to now, the pressing jacket exits the press nip in a large radius that is determined by its own stiffness, centrifugal forces, and the line load of the pressing jacket. Correspondingly, the separation of the paper and the felt does not occur until far outside of the press nip, which has the result that the reverse moistening of the paper occurring up to the separation from the felt is very high, in particular in the case of thinner papers such as tissue papers.
The present invention provides a pressing arrangement of the type mentioned at the outset in which such a reverse moistening is reduced to a minimum and with which a considerably greater dry content of the fibrous material web may be correspondingly achieved.
According to the instant invention, a pressing arrangement is provided for treating a fibrous material web, in particular a paper, cardboard, or tissue web, with a press nip formed between a shoe press roll and an opposing surface is elongated in the web travel direction. The shoe press roll includes a carrier that is mounted in a non-rotational manner, a pressing jacket circulating around the carrier, and at least one press shoe supported on the carrier, such that the flexible pressing jacket may be pressed against the opposing surface. Further, the press shoe is extended in the jacket travel direction past the pressing nip by an outlet, and the pressing jacket is guided through the outlet when the press shoe is pressed against the opposing surface in such a way that, in a region of the press nip, the pressing jacket runs radially outside of the circular path that would result from an assumed constantly cylindrical web guidance and rests against it in the region of the free end of the outlet.
Based on this construction, a reduction of the reverse moistening is attained by a corresponding guidance of the pressing jacket outside of the press nip, which correspondingly leads to a considerably higher dry content of the fibrous material web. After the press shoe is provided with a longer outlet and presses relatively far outside of the undeformed pressing jacket contour in the operational setting, the pressing jacket lies against the region of the end of the outlet during operation and thus seals off the outlet region in an airtight manner. Because this eliminates a ventilation at the rear of the region, the pressing jacket must follow the outlet contour precisely, which brings about an immediate separation of the felt and fibrous material web outside of the pressing nip.
In a preferred embodiment of the pressing arrangement according to the invention, the length of the outlet, viewed in the jacket travel direction, is greater than approximately half the length of the press nip, in particular greater than approximately three quarters of the length of the press nip, and preferably greater than or equal to about the length of the press nip.
When the pressing shoe is pressed against the opposing surface, it is advantageous for the pressing jacket to be guided through it in such a way that it drifts out of the imaginary circular path in the region of the press nip by an amount corresponding on the average to approximately 1 to approximately 3%, in particular approximately 1.5 to approximately 2.5%, and in particular approximately 2% of the diameter of the circular path.
The outlet can have an at least essentially even surface facing the pressing jacket.
It is advantageous for the surface of the outlet facing the pressing jacket, which is at least essentially even, to form an angle in the range of approximately 18xc2x0 with the tangent resting against the pressing surface of the press shoe defining the press nip and facing the pressing jacket on the press nip outlet.
It is useful for the contour of the pressing surface of the press shoe facing the pressing jacket and defining the press nip to be adapted to the contour of the opposing surface.
The opposing surface can be formed, for example, by an opposing roll. Especially in this case, the pressing surface of the press shoe facing the pressing jacket and defining the press nip can therefore have a generally concave contour.
In a useful practical embodiment, the outlet is bent generally radially inwards on its free end. Here, the pressing jacket can rest against the outlet in the preferably rounded transitional region to the end of the outlet, which is generally bent radially inwards.
The invention shall be described in greater detail in the following using an exemplary embodiment with reference to the drawing.
The present invention is directed to a pressing arrangement for treating a fibrous material web. The pressing arrangement includes an opposing surface and a shoe press roll including a non-rotationally mounted carrier, a flexible pressing jacket arranged to circulate around the carrier, and at least one press shoe supported on the carrier. The at least one press shoe is arranged to press the flexible pressing jacket against the opposing surface. The shoe press roll and the opposing surface are arranged to form a press nip elongated in a jacket travel direction, and the at least one press shoe includes an outlet arranged to extend beyond, in the jacket travel direction, an end of the press nip. The at least one press shoe is arranged to press the pressing jacket against the opposing surface such that, in a region of the press nip, the pressing jacket is moved radially outside of a circular path formed by the pressing jacket in an unstressed state, and the pressing jacket is arranged to rest against a free end of the outlet.
In accordance with a feature of the invention, the fibrous material web may include one of a paper, cardboard, or tissue web.
Further, in the jacket travel direction, a length of the outlet may be greater than approximately one-half a length of the press nip. Preferably, the length of the outlet can be greater than approximately three quarters of the length of the press nip, and most preferably, the length of the outlet may be greater than or equal to about the length of the press nip.
Moreover, when the press shoe is pressed against the opposing surface, the pressing jacket, in the region of the press nip, can be moved a distance from the circular path of between approximately 1 to approximately 3% of a diameter of the circular path. Preferably, the distance from circular path moved by the pressing jacket, in the region of the press nip, can be between approximately 1.5 and approximately 2.5% of the diameter of the circular path, and most preferably, the distance from the circular path moved by the pressing jacket, in the region of the press nip, may be approximately 2% of the diameter of the circular path.
According to another feature of the present invention, the outlet may include at least essentially even surface arranged to face the pressing jacket. The at least essentially even surface of the outlet can be arranged to form an angle of approximately 18xc2x0 to a tangent resting against a pressing surface of the at least one press shoe that is arranged to define the press nip. A contour of the pressing surface facing the pressing jacket and defining the press nip can be structured to correspond to a contour of the opposing surface. The opposing surface may be formed by an opposing roll. Further, the pressing surface facing the pressing jacket and defining the pressing nip may be structured with a generally concave contour.
In accordance with still another feature of the invention, the free end of the outlet can be structured to be bent generally radially inwardly.
Moreover, the free end of the outlet can include a rounded transitional region generally bent radially inwardly, and the pressing jacket can be arranged to rest against the outlet.
The pressing arrangement of the instant invention can also include at least one dewatering belt. The fibrous material web may be guided through the press nip along with the at least one dewatering belt. The at least one dewatering belt can include a felt.
The present invention is directed to an apparatus for treating a fibrous material web. The apparatus includes a shoe press roll having a flexible rotatable roll jacket and at least one press shoe arranged to press against an inner surface of the roll jacket and an opposing surface. The shoe press roll and the opposing surface are arranged to form a press nip elongated in a roll jacket travel direction. The press shoe includes a press surface structured and arranged to define the press nip and an outlet surface positioned obliquely adjacent an end of the press surface forming an exit of the press nip, in relation to the roll jacket travel direction. The at least one press shoe is arranged to press the roll jacket against the opposing surface such that, in a press nip region, the pressing jacket is moved radially outside of a circular path formed by the pressing jacket in an unstressed state.
In accordance with a feature of the instant invention, in the roll jacket travel direction, a length of the outlet surface can be greater than approximately one-half a length of the press nip. Further, the length of the outlet surface can be greater than approximately three quarters of the length of the press nip, and the length of the outlet surface may be greater than or equal to about the length of the press nip.
Further, when the press shoe is pressed against the opposing surface, the roll jacket, in the region of the press nip, may be moved a distance from the circular path of between approximately 1 to approximately 3% of a diameter of the circular path. Still further, the distance from circular path moved by the roll jacket, in the region of the press nip, may be between approximately 1.5 and approximately 2.5% of the diameter of the circular path, and the distance from the circular path moved by the pressing jacket, in the region of the press nip, can be approximately 2% of the diameter of the circular path.
According to another feature of the present invention, the outlet surface can be obliquely arranged adjacent the press surface to form an angle of approximately 18xc2x0 to the press surface.
A free end of the outlet surface opposite the press surface may include a rounded transitional region. Further, the rounded transitional region can be structured to be bent radially inwardly.
In accordance with yet another feature of the instant invention, at least one dewatering belt can be structured and arranged to guide the fibrous material web through the press nip.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.